IG window unit including double silver coating having increased SHGC to U-value ratio, and corresponding coated article for use in IG window unit or other window

ABSTRACT

An insulating glass (IG) window unit includes first and second substrates, and a low-emissivity (low-E) coating supported by one of the substrates. The low-E coating has two silver based infrared (IR) reflecting layers and allows the IG window unit to realize an increased SHGC to U-value ratio, and an increased thickness ratio of an upper silver based layer of the coating to a bottom silver based layer of the coating. The low-E coating is designed to have a low film-side reflectance, so that for example when the low-E coating is used on surface number three of an IG window unit the IG window unit can realize reduced visible reflectance as viewed from the outside of the building on which the IG window unit is mounted or is to be mounted.

This application is a continuation of application Ser. No. 15/077,279,filed Mar. 22, 2016 (now U.S. Pat. No. 9,556,070), which is acontinuation of application Ser. No. 14/592,970, filed Jan. 9, 2015,(now Pat. No. 9,302,936), which is a continuation of application Ser.No. 14/016,282 filed Sep. 3, 2013 (now Pat. No. 8,940,400), the entiredisclosures of which are all hereby incorporated herein by reference inthis application.

Certain embodiments of this invention relate to an insulating glass (IG)window unit including a low-emissivity (low-E) coating supported by asubstrate such as a glass substrate, and/or to a corresponding coatedarticle including a low-E coating supported by a glass substrate for usein the IG or other window unit. In certain example embodiments of thisinvention, the low-E coating is designed so as to allow the IG windowunit to realize an increased SHGC to U-value ratio, and an increasedthickness ratio of an upper silver based layer of the coating to abottom silver based layer of the coating. In certain exampleembodiments, the low-E coating is designed to have a low film-sidereflectance, so that for example when the low-E coating is used onsurface number three of an IG window unit the IG window unit can realizereduced visible reflectance as viewed from the outside of the buildingon which the IG window unit is mounted or is to be mounted. In certainexample embodiments, the coated article may or may not be heat treated(e.g., thermally tempered, heat bent and/or heat strengthened).

BACKGROUND OF THE INVENTION

Coated articles are known in the art for use in window applications suchas vehicle windshields, insulating glass (IG) window units, monolithicvehicle windows, and/or the like.

U-value (sometimes referred to as U-factor) is a measure of heat loss ina building element such as a wall, floor, window or roof. It can also bereferred to as an overall heat transfer co-efficient and measures howwell parts of a building transfer heat. This means that the higher theU-value the worse the thermal performance of the building envelope. Alow U-value usually indicates high levels of insulation. In other words,U-value measures how well a product prevents heat from escaping a homeor building. The lower the U-value, the better a product is at keepingheat inside the building. U-value herein is measured in units ofBTU/hr-ft²-° F.), and is calculated according to NFRC 2010 (whichincludes NFRC 100-2010 Winter) at the center of the glazing (COG).U-value as used herein refers to winter/night U-value.

Solar Heat Gain Coefficient (SHGC) measures how much heat from the sunis blocked. SHGC is expressed as a number between 0 and 1. The lower theSHGC, the more a product is blocking solar heat gain. Blocking solarheat gain is particularly important during the summer cooling season inhot climates. However, people in colder climates may want solar heatgain during the cold winter months to lessen the cost of heating thehome. SHGC herein is calculated according to NFRC 2010. SHGC valuesherein are measured in the out→in context of the IG window unit unlessstated otherwise.

Coated articles may or may not be heat treated. The heat treatment (HT)of such coated articles typically requires the use of temperature(s) ofat least 580 degrees C., more preferably of at least about 600 degreesC. and often at least 620 degrees C., for about 5-10 minutes or more,such as for thermal tempering or the like. The terms “heat treatment”and “heat treating” as used herein mean heating the article to atemperature sufficient to achieve thermal tempering, heat bending,and/or heat strengthening of the glass inclusive coated article. Thisdefinition includes, for example, heating a coated article in an oven orfurnace at a temperature of least about 580 degrees C., more preferablyat least about 600 degrees C., for a sufficient period to allowtempering, bending, and/or heat strengthening. In certain instances, theHT may be for at least about 4 or 5 minutes or more.

BRIEF SUMMARY OF EXAMPLE EMBODIMENTS OF THE INVENTION

It is desirable in regions having colder climates (e.g., Canada,Scandinavia, Northern United States, etc.) to have windows with a low-Ecoating which can realize one or more of and preferably a combination ofall of: (i) an IG window unit having high visible transmission such asat least about 70%, (ii) an IG window unit having a high SHGC value suchas at least 0.50, more preferably at least 0.52, even more preferably atleast 0.54 or 0.56, with an example ranges being from about 0.50 to0.60, in the out→in context of the IG window unit when the low-E coatingis on surface three of the IG window unit as shown in FIG. 2, (iii) anIG window unit having a low outdoor/outside reflectance such as nogreater than 15%, such as the low-E coating realizing low film-sidereflectance when used on surface three of an IG window unit so thatreflectance as viewed from the outside of the building is small, (iv)low emissivity and/or low sheet resistance, such as normal emissivity ofno greater than 4% and more preferably no greater than 3%, (v) an IGwindow unit having an acceptable U-value such as a double glazing IGwindow unit with one low-E coating having a U-value of no greater than0.253 BTU/hr-ft²-° F., more preferably no greater than 0.251BTU/hr-ft²-° F., even more preferably no greater than 0.249 BTU/hr-ft²-°F., even more preferably no greater than 0.248 BTU/hr-ft²-° F., with anexample range being from 0.244 to 0.253, more preferably from 0.244 to0.251 BTU/hr-ft²-° F., and (vi) a high SHGC to U-value ratio, calculatedas SHGC/U-Value, of at least 2.0, more preferably of at least 2.10, evenmore preferably of at least 2.15, even more preferably of at least 2.20,and most preferably of at least 2.21, and most preferably of at least2.24.

Conventional double silver low-E coatings (i.e., low-E coatings havingtwo silver-based IR reflecting layers, in addition to other layers suchas dielectric layers) have been developed to increase Light to SolarGain (LSG) coefficient, meaning that the ratio of transmitted light overtransmission of solar energy is maximized. Common LSG ratios of doublesilver low-E coatings range from 1.6 to 1.8, while the thermalinsulation coefficient (U-value) of some is between 0.244 and 0.252.Most double silver coatings have the thicknesses of the silver layersnearly similar, with ratios of upper to lower Ag from 0.8 to 1.2.However, conventional double silver low-E coatings have low SHGC valuesand often high film-side reflectance and thus are undesirable in coldclimates. For example, U.S. Pat. No. 8,142,622 teaches that low SHGCvalues are desirable and achieved with double-silver low-E coatings,thereby teaching away from the instant invention.

Conversely, conventional single Ag coatings (i.e., a low-E coatinghaving just one silver-based IR reflecting layer, in addition to otherlayers such as dielectric layers) have been able to realize maximumsolar transmission while maintaining acceptable U-value from 0.260 to0.280 BTU/hr-ft²-° F. While increasing the Ag layer thickness canimprove the U-value, it would undesirably decrease the Solar Heat GainCoefficient (SHGC) and increase visible reflection (e.g., film sidereflectance) which can both be undesirable. These coatings provide thecurrent preferred solutions for cold climates and perform best perQuebec standards and requirements, though the U-value is greater thanthat of double silver coatings. However, in cold climates it is oftendesired to have a high SHGC, and it is also often desirable to haverelatively low film-side reflectance for a coating so that the coatingmay be used on surface number three of an IG window unit, so thatpassive heat from the sun can makes its way into the building in orderto help heat the building. Accordingly, conventional single silver low-Ecoatings cannot achieve a combination of a high SHGC to U-value ratiotogether with a low U-value and a low film-side reflectance. U.S. Pat.No. 8,409,717 discloses a single silver low-E coating, but it hasundesirably high U-values. In particular, FIG. 3 of U.S. Pat. No.8,409,717 shows that an IG window unit with this single silver coatingsuffers from high U-values of from 0.271 to 0.280.

Thus, it will be apparent that there is a need in the art for a windowwith a low-E coating that can realize one or more of, more preferably atleast four or five of, and most preferably all six of: (i) an IG windowunit having high visible transmission such as at least about 70%, (ii)an IG window unit having a high SHGC value such as at least 0.50, morepreferably at least 0.52, even more preferably at least 0.54, even morepreferably at least 0.56, with an example range being from about 0.50 to0.60, in the out→in context of the IG window unit when the low-E coatingis on surface three of the IG window unit as shown in FIG. 2, (iii) anIG window unit having a low outdoor/outside visible reflectance such asno greater than 15%, such as the low-E coating realizing low film-sidereflectance when used on surface three of an IG window unit so thatreflectance as viewed from the outside of the building is small, (iv)low emissivity and/or low sheet resistance, such as normal emissivity ofno greater than 4% and more preferably no greater than 3%, (v) an IGwindow unit having an acceptable U-value such as a double glazing IGwindow unit with one low-E coating having a U-value of no greater thanabout 0.253 BTU/hr-ft²-° F., more preferably no greater than about 0.251BTU/hr-ft²-° F., more preferably no greater than about 0.249, with anexample range being from 0.244 to 0.253, more preferably from about0.244 to 0.251 BTU/hr-ft²-° F., and (vi) a high SHGC to U-value ratio,calculated as SHGC/U-Value, of at least 2.0, more preferably of at least2.10, even more preferably of at least 2.15, even more preferably of atleast 2.20, more preferably at least 2.21, and most preferably of atleast 2.24. Again, U-value herein is calculated according to NFRC 2010at the center of the glazing (COG). And SHGC herein is calculatedaccording to NFRC 2010, and is measured in this paragraph and otherwiseherein in the out→in context of the IG window unit unless expresslystated otherwise. Example embodiments of this invention fulfill one ormore of these needs, more preferably at least four or five of, and mostpreferably all six of these needs. In order to provide an advantageouscombination of high visible transmission and high SHGC, in certainexample embodiments of this invention, the ratio of the thickness of thebottom silver based IR reflecting layer to the thickness of the topsilver based IR reflecting layer is from 0.30 to 0.50, more preferablyfrom 0.38 to 0.47.

In certain example embodiments of this invention, there is provided aninsulating glass (IG) window unit comprising: first and second glasssubstrates that are spaced apart from each other with a gap therebetweenand substantially parallel to each other, wherein the first glasssubstrate is adapted to be at a building exterior and the second glasssubstrate is adapted to be closer to a building interior than is thefirst glass substrate; a low-E coating on a major surface of the secondglass substrate facing said gap; the low-E coating comprising, movingaway from the second glass substrate: (a) a dielectric layer comprisingsilicon nitride; (b) a dielectric layer comprising titanium oxide; (c) afirst lower contact layer comprising zinc oxide; (d) a first IRreflecting layer comprising silver located over and directly contactingthe first lower contact layer; (e) a first upper contact layer locatedover and directly contacting the first IR reflecting layer comprisingsilver; (f) a layer comprising zinc stannate; (g) a second lower contactlayer comprising zinc oxide; (h) a second IR reflecting layer comprisingsilver located over and directly contacting the second lower contactlayer; (i) a second upper contact layer located over and directlycontacting the second IR reflecting layer comprising silver; and (j) adielectric layer; wherein the low-E coating has only two IR reflectinglayers comprising silver, and wherein the low-E coating has a normalemissivity of no greater than 0.04, and wherein the IG window unit hasonly two glass substrates; wherein a ratio of a thickness of the firstIR reflecting layer comprising silver to a thickness of the second IRreflecting layer comprising silver, calculated as the thickness of thefirst IR reflecting layer comprising silver divided by the thickness ofthe second IR reflecting layer comprising silver, is from 0.30 to 0.50;and wherein the IG window unit has each of: (i) a visible transmissionof at least about 69.5%, (ii) an SHGC value of at least 0.50, (iii) anoutside visible reflectance of no greater than 15%, (iv) a U-value of nogreater than 0.253 BTU/hr-ft²-° F., and (v) a ratio calculated asSHGC/U-Value of at least 2.0.

In certain example embodiments of this invention, there is provided aninsulating glass (IG) window unit comprising: first and second glasssubstrates that are spaced apart from each other with a gap therebetweenand substantially parallel to each other, wherein the first glasssubstrate is adapted to be at a building exterior and the second glasssubstrate is adapted to be closer to a building interior than is thefirst glass substrate; a low-E coating on a major surface of the secondglass substrate facing said gap; the low-E coating comprising, movingaway from the second glass substrate: (a) a dielectric layer; (b) afirst lower contact layer comprising zinc oxide; (c) a first IRreflecting layer comprising silver located over and directly contactingthe first lower contact layer; (d) a first upper contact layer locatedover and directly contacting the first IR reflecting layer comprisingsilver; (e) a layer comprising tin oxide and/or zinc stannate; (f) asecond lower contact layer comprising zinc oxide; (g) a second IRreflecting layer comprising silver located over and directly contactingthe second lower contact layer; (h) a second upper contact layer locatedover and directly contacting the second IR reflecting layer comprisingsilver; and (i) another dielectric layer; wherein the low-E coating hasa normal emissivity of no greater than 0.04; wherein a ratio of athickness of the first IR reflecting layer comprising silver to athickness of the second IR reflecting layer comprising silver,calculated as the thickness of the first IR reflecting layer comprisingsilver divided by the thickness of the second IR reflecting layercomprising silver, is from 0.30 to 0.50; and wherein the IG window unithas each of: (i) a visible transmission of at least about 69.5%, (ii) anSHGC value of at least 0.50, (iii) an outside visible reflectance of nogreater than 15%, and (iv) a U-value of no greater than about 0.253BTU/hr-ft²-° F.

In certain example embodiments of this invention, there is provided aninsulating glass (IG) window unit comprising: first and second glasssubstrates that are spaced apart from each other with a gap therebetweenand substantially parallel to each other, wherein the first glasssubstrate is adapted to be at a building exterior and the second glasssubstrate is adapted to be closer to a building interior than is thefirst glass substrate; a low-E coating on a major surface of the secondglass substrate facing said gap; the low-E coating comprising, movingaway from the second glass substrate: a dielectric layer; a first lowercontact layer comprising zinc oxide; a first IR reflecting layercomprising silver located over and directly contacting the first lowercontact layer; a first upper contact layer located over and directlycontacting the first IR reflecting layer comprising silver; a layercomprising tin oxide and/or zinc stannate; a second lower contact layercomprising zinc oxide; a second IR reflecting layer comprising silverlocated over and directly contacting the second lower contact layer; asecond upper contact layer located over and directly contacting thesecond IR reflecting layer comprising silver; and another dielectriclayer; wherein the low-E coating has a normal emissivity of no greaterthan 0.04; wherein a ratio of a thickness of the first IR reflectinglayer comprising silver to a thickness of the second IR reflecting layercomprising silver, calculated as the thickness of the first IRreflecting layer comprising silver divided by the thickness of thesecond IR reflecting layer comprising silver, is from 0.30 to 0.50; andwherein the IG window unit has each of: (i) a visible transmission of atleast about 69.5%, (ii) an SHGC value of at least 0.50, (iii) an outsidevisible reflectance of no greater than 15%, and (iv) a ratio calculatedas SHGC/U-Value of at least 2.20 (more preferably at least 2.24), whereU-value is in units of BTU/hr-ft²-° F.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view of a coated article according to anexample embodiment of this invention.

FIG. 2 is a cross sectional view of an IG window unit including thecoated article of FIG. 1 on surface three of the IG window unitaccording to an example embodiment of this invention.

FIG. 3 is a graph plotting bottom/top silver based layer ratio for thehorizontal axis values vs. SHGC and visible transmission (Tvis) for thevertical axis values, including a plot (upper contour line) for Tvisvalues and a plot (lower contour line) for SHGC values.

DETAILED DESCRIPTION OF EXAMPLES OF THE INVENTION

Coated articles herein may be used in applications such as IG ormonolithic window units.

Certain example embodiments of this invention relate to a low-E coating30 used in connection with a coated article and/or IG window unit.

FIG. 1 is a side cross sectional view of a coated article according toan example non-limiting embodiment of this invention. The coated articleincludes substrate 1 (e.g., clear, green, bronze, or blue-green glasssubstrate from about 1.0 to 10.0 mm thick, more preferably from about1.0 mm to 3.5 mm thick), and coating (or layer system) 30 provided onthe substrate 1 either directly or indirectly. The low-E coating (orlayer system) 30 is a double-silver low-E coating and includes: bottomsilicon nitride inclusive dielectric layer 3 which may be Si₃N₄, of theSi-rich type for haze reduction, or of any other suitable stoichiometryin different embodiments of this invention, transparent dielectric layer5 of or including titanium oxide (e.g., TiO₂ or any other suitablestoichiometry), transparent first lower contact layer 7 (which contactsbottom silver-based IR reflecting layer 9), first conductive andpreferably metallic infrared (IR) reflecting layer 9 of or includingsilver, transparent first upper contact layer 11 (which contacts layer9), transparent dielectric layer 14 of or including zinc stannate,transparent dielectric layer 15 of or including tin oxide, transparentsecond lower contact layer 17 (which contacts silver-based IR reflectinglayer 19), second conductive and preferably metallic IR reflecting layer19 of or including silver, transparent second upper contact layer 21(which contacts layer 19), transparent dielectric layer 23, andtransparent silicon nitride inclusive layer 25. The “contact” layers 7,11, 17 and 21 each contact at least one infrared (IR) reflecting layer(e.g., layer based on Ag). The aforesaid layers 3-25 make up low-E(i.e., low emissivity) coating 30 which is provided on glass or plasticsubstrate 1. The layers 3-25 of coating 30 may be sputter-deposited onthe substrate 1 in certain example embodiments of this invention.

In monolithic instances, the coated article includes only one glasssubstrate 1 as illustrated in FIG. 1. However, monolithic coatedarticles herein may be used in devices such as IG window units, and thelike. As for IG window units, an IG window unit may include two spacedapart glass substrates. An example IG window unit is illustrated anddescribed, for example, in U.S. Patent Document No. 2004/0005467, thedisclosure of which is hereby incorporated herein by reference. FIG. 2shows an example IG window unit including the coated glass substrate 1shown in FIG. 1 coupled to another glass substrate 2 via spacer(s),sealant(s)/spacer(s) 40 or the like, with a gap 50 being definedtherebetween. This gap 50 between the substrates in IG window unitembodiments may in certain instances be filled with a gas such as argon(Ar). An example IG unit may comprise a pair of spaced apart clear glasssubstrates each about 3-4 mm thick, one of which is coated with acoating 30 herein in certain example instances, where the gap 50 betweenthe substrates may be from about 5 to 30 mm, more preferably from about10 to 20 mm, and most preferably about 12-13 mm or 16 mm. In certainexample instances, the low-E coating 30 may be provided on surface threeof the IG window unit as shown in FIG. 2. When the low-E coating 30 ison surface three, which is particularly desired in cold climates, thecoating 30 is on the major surface of the inner substrate 1 that facesthe gas-filled gap 50 as shown in FIG. 2. In alternative exampleembodiments the coating 30, or another coating, may be provided onsurface two of the IG window unit which is the interior surface of glasssubstrate 2. Surface one of the IG window unit is at the buildingexterior, and surface four is at the building interior, as shown in FIG.2.

Dielectric layers 3 and 25 may be of or include silicon nitride incertain embodiments of this invention. Silicon nitride layers 3 and 25may, among other things, improve heat-treatability of the coatedarticles, e.g., such as thermal tempering or the like, and may or maynot include some oxygen. The silicon nitride of layers 3 and/or 25 maybe of the stoichiometric type (i.e., Si₃N₄), or alternatively of theSi-rich type in different embodiments of this invention. For example,Si-rich silicon nitride 3 (and/or 25) combined with zinc stannate 14and/or tin oxide 15 under a silver based IR reflecting layer 19 maypermit the silver to be deposited (e.g., via sputtering or the like) ina manner which causes its sheet resistance to be lessened compared to ifcertain other material(s) were under the silver. Moreover, the presenceof free Si in a Si-rich silicon nitride inclusive layer 3 may allowcertain atoms such as sodium (Na) which migrate outwardly from the glass1 during heat treatment (HT) to be more efficiently stopped by theSi-rich silicon nitride inclusive layer before they can reach the silverand damage the same.

In certain example embodiments, when Si-rich silicon nitride is used inlayer 3 and/or 25, the Si-rich silicon nitride layer as deposited may becharacterized by Si_(x)N_(y) layer(s), where x/y may be from 0.76 to1.5, more preferably from 0.8 to 1.4, still more preferably from 0.85 to1.2. Moreover, in certain example embodiments, before and/or after HTthe Si-rich Si_(x)N_(y) layer(s) may have an index of refraction “n” ofat least 2.05, more preferably of at least 2.07, and sometimes at least2.10 (e.g., 632 nm) (note: stoichiometric Si₃N₄ which may also be usedhas an index “n” of 2.02-2.04). It has also surprisingly been found thatusing Si-rich silicon nitride, with a refractive index “n” of from 2.1to 2.2 for layer 3, results in more neutral transmitted and reflectedcoloration of the coated article and IG window unit. Any and/or all ofthe silicon nitride layers 3, 25 discussed herein may be doped withother materials such as stainless steel or aluminum in certain exampleembodiments of this invention. For example, any and/or all siliconnitride layers discussed herein may optionally include from about 0-15%aluminum, more preferably from about 1 to 10% aluminum, in certainexample embodiments of this invention. The silicon nitride may bedeposited by sputtering a target of Si or SiAl in an atmosphereincluding at least nitrogen gas in certain embodiments of thisinvention. Small amounts of oxygen may also be provided in layer(s) 3and/or 25.

Infrared (IR) reflecting layers 9 and 19 are preferably substantially orentirely metallic and/or conductive, and may comprise or consistessentially of silver (Ag). IR reflecting layers 9 and 19 help allow thecoating to have low-E and/or good solar control characteristics. The IRreflecting layers may, however, be slightly oxidized in certainembodiments of this invention and may be doped with other element(s) inaddition to the silver.

The upper contact layers 11 and 21 may be of or include nickel (Ni)oxide, chromium/chrome (Cr) oxide, or a nickel alloy oxide such asnickel chrome oxide (NiCrO_(x)), or other suitable material(s), incertain example embodiments of this invention. The use of, for example,NiCrO_(x) in these layers (11 and/or 21) allows durability to beimproved. The NiCrO_(x) of layers 11 and/or 21 may be fully oxidized incertain embodiments of this invention (i.e., fully stoichiometric), oralternatively may only be partially oxidized (i.e., sub-oxide). Incertain instances, the NiCrO_(x) layers 11 and/or 21 may be at leastabout 50% oxidized. Contact layers 11 and/or 21 (e.g., of or includingan oxide of Ni and/or Cr) may or may not be oxidation graded indifferent embodiments of this invention. Oxidation grading means thatthe degree of oxidation in the layer changes throughout the thickness ofthe layer. For example, a contact layer 11 and/or 21 may be graded so asto be less oxidized at the contact interface with the immediatelyadjacent IR reflecting layer than at a portion of the contact layer(s)further or more/most distant from the immediately adjacent IR reflectinglayer. Descriptions of various types of oxidation graded contact layersare set forth in U.S. Pat. No. 6,576,349, the disclosure of which ishereby incorporated herein by reference. Contact layers 11 and/or 21(e.g., of or including an oxide of Ni and/or Cr) may or may not becontinuous in different embodiments of this invention across the entireunderlying IR reflecting layer.

Dielectric layer 15 may be of or include tin oxide in certain exampleembodiments of this invention. However, it may be doped with certainother materials in other example embodiments, such as with Al or Zn incertain example alternative embodiments. Moreover, zinc stannateinclusive layer 14 may be omitted, or replaced with a tin oxide basedlayer (e.g., which may be doped with Al or the like), or may be dopedwith other material(s) such as Al, Nb, Bi or the like, in certainexample embodiments of this invention. Additionally, transparentdielectric layer 15 may be of or include tin oxide as explained herein,and may be doped with other material(s) such as Al, Bi, and/or Nb.Alternatively, transparent dielectric layer 15 may be of or includeniobium oxide (instead of tin oxide) in certain example embodiments ofthis invention, which may or may not be doped with other material(s).

Dielectric layer 5 of or including titanium oxide (e.g., TiO₂ or anyother suitable stoichiometry) is provided for optical purposes, and itsposition between silicon nitride inclusive layer 3 and zinc oxide basedlayer 7 is helpful for antireflective purposes. Likewise, the two Agbased layers 9, 19 are also beneficial for antireflective purposes.

Lower contact layers 7 and/or 17 in certain embodiments of thisinvention are of or include zinc oxide (e.g., ZnO). The zinc oxide oflayers 7 and/or 17 may contain other materials as well such as Al (e.g.,to form ZnAlO_(x)). For example, in certain example embodiments of thisinvention, one or more of zinc oxide layers 7, 17 may be doped with fromabout 1 to 10% Al, more preferably from about 1 to 5% Al, and mostpreferably about 1 to 4% Al. In certain example embodiments, the lowercontact layer 7 comprising ZnO and/or ZnAlO is thicker than the uppercontact layer 17 comprising ZnO and/or ZnAlO by at least about 30 Å,more preferably by at least about 50 Å.

Zinc stannate based layer 14 is provided under and contacting layer 15comprising tin oxide, and over and possibly contacting contact layer 11,in a central portion of the layer stack between first and second IRreflecting layers 9 and 19. In certain example embodiments, it ispossible to dope the zinc stannate based layer 14 and/or tin oxide basedlayer 15 with other materials such as Al, Zn, N, or the like.

Dielectric layer 23 may be of or include tin oxide in certain exampleembodiments of this invention. However, layer 23 is optional and neednot be provided in certain example embodiments of this invention.Dielectric layer 25 may be of or include silicon nitride (e.g., Si₃N₄)or any other suitable material in certain example embodiments of thisinvention. Optionally, other layers may be provided above layer 25.Layer 25 is provided for durability purposes, and to protect theunderlying layers during optional heat treatment and/or environmentaluse. In certain example embodiments, layer 25 may have an index ofrefraction (n) of from about 1.9 to 2.2, more preferably from about 1.95to 2.05. Optionally, the provision of an overcoat layer of or includingzirconium oxide (not shown) as an overcoat for the coating 30 can reduceand/or eliminate certain thermal stability issues.

In certain example embodiments, it has been found that good opticalproperties are achieved when the total thickness of the combination ofzinc stannate based layer 14 and tin oxide inclusive layer 15 is fromabout 600 to 900 Å, more preferably from about 700 to 800 Å. All layerthicknesses referred to herein are physical thicknesses. In certainexample embodiments, zinc stannate based layer 14 is substantiallythicker than is tin oxide based layer 15. For example, in certainexample embodiments, zinc stannate layer 14 is thicker than tin oxidebased layer 15 by at least about 300 Å, more preferably by at least 400or 500 Å. Each of layers 14 and 15 is substantially thicker than contactlayer 11 in certain example embodiments of this invention. For example,in certain example embodiments, zinc stannate based layer 14 and tinoxide based layer 15 are each thicker than contact layer 11 by at leastabout 40 Å, more preferably by at least 50 Å.

Other layer(s) below or above the illustrated coating may also beprovided. Thus, while the layer system or coating is “on” or “supportedby” substrate 1 (directly or indirectly), other layer(s) may be providedtherebetween. Thus, for example, the coating of FIG. 1 may be considered“on” and “supported by” the substrate 1 even if other layer(s) areprovided between layer 3 and substrate 1. Moreover, certain layers ofthe illustrated coating may be removed in certain embodiments, whileothers may be added between the various layers or the various layer(s)may be split with other layer(s) added between the split sections inother embodiments of this invention without departing from the overallspirit of certain embodiments of this invention. For example, layer 5may be removed in example embodiments of this invention. As anotherexample, a layer of or including silicon nitride may be provided oneither side of layer 15 in example embodiments of this invention.

Referring to FIG. 3, analysis of double-silver low-E coatingsdemonstrates that there is a peak area for SHGC that is based on thethickness ratio of the bottom silver-based layer 9 to the top silverbased layer 19. It has been found that the highest SHGC for adouble-silver low-E coating is realized in an area where the ratio ofthe physical thickness of the bottom silver-based layer 9 to thephysical thickness of the top silver-based layer 19 is from 0.20 to0.50. However, the visible transmission of the coating is rather low inthe area where this ratio is from 0.20 to 0.30. Thus, it has been foundthat the optimum results for high visible transmission in combinationwith high SHGC are achieved in the range where the ratio of the physicalthickness of the bottom silver-based layer 9 to the physical thicknessof the top silver-based layer 19 is from 0.30 to 0.50 (see therectangular box in FIG. 3). This is particularly desirable forapplications in cold climates as explained herein. Thus, in certainexample embodiments of this invention, desirable thermal and opticalcharacteristics are achieved utilizing this range in combination withother factors discussed herein. Thus, in preferred embodiments of thisinvention, the ratio of the thickness of the bottom IR reflecting layer9 to the thickness of the top IR reflecting layer 19 is from 0.30 to0.50, more preferably from 0.38 to 0.47. For example, if the bottomsilver based IR reflecting layer 9 is 52 Å thick and the upper/topsilver based IR reflecting layer 19 is 116 Å thick, then the ratio ofthe thickness of the bottom IR reflecting layer 9 to the thickness ofthe top IR reflecting layer 19 is 0.45 which is within the preferredrange.

The IG unit of FIG. 2, which includes the coated article of FIG. 1 asdescribed above, has surprisingly been found to be able to achieve acombination of the following advantageous features which areparticularly desirable in cold climate applications: (i) an IG windowunit having high visible transmission such as at least about 70%, (ii)an IG window unit having a high SHGC value such as at least 0.50, morepreferably at least 0.52, more preferably at least 0.54, even morepreferably at least 0.56, with an example range being from about 0.50 to0.60, in the out→in context of the IG window unit when the low-E coatingis on surface three of the IG window unit as shown in FIG. 2, (iii) anIG window unit having a low outdoor/outside reflectance such as nogreater than 15%, such as the low-E coating realizing low film-sidereflectance when used on surface three of an IG window unit so thatreflectance as viewed from the outside of the building is small, (iv)low emissivity and/or low sheet resistance, such as normal emissivity ofno greater than 4% and more preferably no greater than 3%, (v) an IGwindow unit having an acceptable U-value such as a double glazing IGwindow unit with one low-E coating having a U-value of no greater than0.253, more preferably no greater than 0.251, even more preferably nogreater than 0.249, with an example range being from 0.244 to 0.253,more preferably from about 0.244 to 0.251, and (vi) a high SHGC toU-value ratio, calculated as SHGC/U-Value, of at least 2.0, morepreferably of at least 2.10, even more preferably of at least 2.15, evenmore preferably of at least 2.20, even more preferably at least 2.21,and most preferably of at least 2.24.

While the IG unit of FIG. 1 is preferably used on surface three of an IGwindow unit as shown in FIG. 2, the coating of FIG. 1 may also be usedon surface two of an IG window unit in certain example embodiments ofthis invention. The U-value (U-factor) would not be affected betweensurface two and surface three, and in an example where the coating 30 ison surface two of the IG window unit (on the interior surface ofsubstrate 2 facing gap 50) the unit could have an SHGC of about 0.468 orthe like.

While various thicknesses and materials may be used in layers indifferent embodiments of this invention, example thicknesses andmaterials for the respective layers on the glass substrate 1 in the FIG.1-2 embodiment are as follows, from the glass substrate outwardly:

Example Materials/Thicknesses; FIG. 1-2 Embodiment Layer Preferred MoreGlass (1-10 mm thick) Range ({acute over (Å)}) Preferred ({acute over(Å)}) Example (Å) Si_(x)N_(y) (layer 3) 40-450 Å 130-250 Å 180 Å TiO_(x)(layer 5) 40-250 Å  60-110 Å  80 Å ZnAlO_(x) (layer 7) 100-180 {acuteover (Å)}  130-170 {acute over (Å)} 150 Å Ag (layer 9)  40-75 {acuteover (Å)}  45-65 {acute over (Å)}  52 Å NiCrO_(x) (layer 11)  10-60{acute over (Å)}  25-40 {acute over (Å)}  30 Å ZnSnO (layer 14) 300-900Å  550-800 Å 650 Å SnO₂ (layer 15) 40-250 Å  50-150 Å 100 Å ZnAlO_(x)(layer 17) 50-120 {acute over (Å)}  70-95 {acute over (Å)}  82 Å Ag(layer 19) 85-145 {acute over (Å)} 105-130 {acute over (Å)} 116 ÅNiCrO_(x) (layer 21)  10-60 {acute over (Å)}  20-40 {acute over (Å)}  30Å SnO₂ (layer 23)  0-500 Å 150-270 Å 220 Å Si₃N₄ (layer 25) 100-450{acute over (Å)}  150-260 {acute over (Å)} 210 Å

In certain example embodiments of this invention (e.g., see FIGS. 1-2),coated articles herein may have the following optical and solarcharacteristics when measured monolithically (before any optional HT).The sheet resistances (R_(s)) and emissivity values herein take intoaccount all IR reflecting layers (e.g., silver layers 9, 19). In thechart below, as will be appreciated by those skilled in the art, “f”refers to film side and “g” refers to glass side and “t” stands fortransmissive, while R refers to reflectance.

Optical/Solar Characteristics (Monolithic; pre-HT) CharacteristicGeneral More Preferred R_(s) (ohms/sq.):  <=5.0 <=4.0 E_(n): <=0.04 (4%)<=0.03 (3%) T_(vis) (or TY)(Ill. C 2°): >=70% >=76%  a*_(t) (Ill. C 2°):−4.0 to +1.0 −2.5 to 0    b*_(t) (Ill. C 2°):    0 to +5.0 +1.0 to +3.5R_(f)Y (Ill. C, 2 deg.):  <=8% <=6.5% or <=5.0% a*_(f) (Ill. C, 2°):−6.0 to +5.0 −5.0 to +3.0 b*_(f) (Ill. C, 2°): −15.0 to 0     −12.0 to0     R_(g)Y (Ill. C, 2 deg.): <=11%   <=9.5% a*_(g) (Ill. C, 2°): −6.0to +2.0 −4.0 to +1.0 b*_(g) (Ill. C, 2°): −20.0 to 0     −15.0 to −3.0 

Note the low film side visible reflectance values (R_(f)Y) in the chartabove, which can be achieved by example embodiments of this invention,which are particularly desirable in cold climates where the low-Ecoating is used on surface three of an IG window unit. In certainexample embodiments, measured monolithically, film side visiblereflectance (R_(f)Y) is lower than glass side visible reflectance(R_(g)Y) which is particularly desirable in such cold climateapplications.

When the monolithic coated article is provided in an IG window unit, onsurface three as shown in FIG. 2, the IG window unit in certain exampleembodiments of this invention (e.g., see FIGS. 1-2) may have thefollowing optical and solar characteristics.

Optical/Solar Characteristics (IG Unit; non-HT) Characteristic GeneralMore Preferred R_(s) (ohms/sq.):  <=5.0  <=4.0 E_(n): <=0.04 (4%) <=0.03(3%) SHGC (outside→in): 0.50 to 0.60 0.53 to 0.60 SHGC (inside→out):0.40 to 0.50 0.45 to 0.49 U-value (winter/COG): 0.230 to 0.253 0.244 to0.251 BTU/ hr-ft²-° F. T_(vis) (or TY)(Ill. C 2°):   >=69.5% >=71%a*_(t) (Ill. C 2°): −4.0 to +1.0 −3.0 to 0    b*_(t) (Ill. C 2°):    0to +5.0 +1.0 to +3.5 R_(outside)Y (Ill. C, 2 deg.): <=15% <=14%a*_(outside) (Ill. C, 2°): −5.0 to +4.0 −3.0 to +2.0 b*_(outside) (Ill.C, 2°): −10.0 to 0     −8.0 to 0    R_(inside)Y (Ill. C, 2 deg.): <=17%<=15% a*_(inside) (Ill. C, 2°): −4.5 to +2.0 −3.5 to −0.5 b*_(inside)(Ill. C, 2°): −15.0 to 0     −11.0 to −1.0 Note the low visible reflectance values to be viewed from the outside ofthe building (R_(outside)Y) in the chart above, which can be achieved byexample embodiments of this invention, which are particularly desirablein cold climates where the low-E coating is used on surface three of anIG window unit. In certain example embodiments, visible reflectance tobe viewed from the outside of the building in which the IG unit is to bemounted (R_(outside)Y) is lower than the visible reflectance(R_(inside)Y) to be viewed from the inside of the building.

The following example is provided for purposes of example only, and isnot intended to be limiting unless specifically claimed.

EXAMPLE 1

The following Example was made via sputtering on a 3.0 mm thick clearglass substrate 1 so as to have approximately the layer stack set forthbelow. This example is according to an example embodiment of thisinvention as shown in FIG. 1. The thicknesses are in units of angstroms(Å) and are approximations.

Layer Glass Substrate Example 1 Si_(x)N_(y) 150 TiO₂ 108 ZnAlO 150 Ag 56NiCrO_(x) 30 ZnSnO 650 SnO₂ 100 ZnAlO 82 Ag 116 NiCrO_(x) 30 SnO₂ 220Si₃N₄ 220

The coated article of Example 1 had the following characteristicsmeasured monolithically:

Optical/Solar Characteristics (Ex. 1 monolithic; pre-HT) CharacteristicValue T_(vis) (or TY)(Ill. C 2°): 79.5% a*_(t) (Ill. C 2°): −1.01 b*_(t)(Ill. C 2°): +2.32 R_(f)Y (Ill. C, 2 deg.): 6.1% a*_(f) (Ill. C, 2°):+1.8 b*_(f) (Ill. C, 2°): −9.78 R_(g)Y (Ill. C, 2 deg.): 8.8% a*_(g)(Ill. C, 2°): −0.69 b*_(g) (Ill. C, 2°): −12.56

After being sputter deposited onto the glass substrate as shown in FIG.1, the Example coated article was not thermally tempered and wasprovided on surface three of an IG window unit as shown in FIG. 2, wherethe second glass substrate 2 was uncoated, clear and 3 mm thick. The gap50 between the glass substrates 1 and 2 of the IG window unit was 90%argon gas and 10% air filled, and was about 13 mm thick/wide. The IGunit had the following characteristics:

Optical/Solar Characteristics (Ex. 1 IG Unit; non-HT) CharacteristicValue SHGC (outside→in): 0.548 SHGC (inside→out): 0.470 U-value(winter/COG): 0.247 BTU/hr-ft²-° F. LSG (outside→in): 1.32 LSG(inside→out): 1.53 T_(vis) (or TY)(Ill. C 2°): 72.1% a*_(t) (Ill. C 2°):−1.64 b*_(t) (Ill. C 2°): +2.22 R_(outside)Y (Ill. C, 2 deg.): 13.1%a*_(outside) (Ill. C, 2°): +0.35 b*_(outside) (Ill. C, 2°): −5.46R_(inside)Y (Ill. C, 2 deg.): 14.0% a*_(inside) (Ill. C, 2°): −1.05b*_(inside) (Ill. C, 2°): −9.09

This performance, including the combination of low U-value, high visibletransmission, high SHGC, and low outside reflectance, is better than anyknown product on the market as of the filing of this application.

In certain example embodiments of this invention, there is provided aninsulating glass (IG) window unit comprising: first and second glasssubstrates that are spaced apart from each other with a gap therebetweenand substantially parallel to each other, wherein the first glasssubstrate is adapted to be at a building exterior and the second glasssubstrate is adapted to be closer to a building interior than is thefirst glass substrate; a low-E coating on a major surface of the secondglass substrate facing said gap; the low-E coating comprising, movingaway from the second glass substrate: (a) a dielectric layer comprisingsilicon nitride; (b) a dielectric layer comprising titanium oxide; (c) afirst lower contact layer comprising zinc oxide; (d) a first IRreflecting layer comprising silver located over and directly contactingthe first lower contact layer; (e) a first upper contact layer locatedover and directly contacting the first IR reflecting layer comprisingsilver; (h) a layer comprising zinc stannate; (g) a second lower contactlayer comprising zinc oxide; (h) a second IR reflecting layer comprisingsilver located over and directly contacting the second lower contactlayer; (i) a second upper contact layer located over and directlycontacting the second IR reflecting layer comprising silver; and (j) adielectric layer; wherein the low-E coating has only two IR reflectinglayers comprising silver, and wherein the low-E coating has a normalemissivity of no greater than 0.04, and wherein the IG window unit hasonly two glass substrates; wherein a ratio of a thickness of the firstIR reflecting layer comprising silver to a thickness of the second IRreflecting layer comprising silver, calculated as the thickness of thefirst IR reflecting layer comprising silver divided by the thickness ofthe second IR reflecting layer comprising silver, is from 0.30 to 0.50;and wherein the IG window unit has each of: (i) a visible transmissionof at least about 69.5%, (ii) an SHGC value of at least 0.50, (iii) anoutside visible reflectance of no greater than 15%, (iv) a U-value of nogreater than 0.253 BTU/hr-ft²-° F., and (v) a ratio calculated asSHGC/U-Value of at least 2.0.

In the IG window unit of the immediately preceding paragraph, the low-Ecoating may have a sheet resistance (R_(s)) of less than or equal to 4.0ohms/square.

The IG window unit of any of the preceding two paragraphs may optionallyhave an SHGC value of at least 0.52, more preferably of at least 0.54,and even more preferably of at least 0.56.

The IG window unit of any of the preceding three paragraphs mayoptionally have an SHGC value of from 0.50 to 0.60.

The IG window unit of any of the preceding four paragraphs mayoptionally have only one low-E coating (i.e., not multiple low-Ecoatings on multiple surfaces).

The IG window unit of any of the preceding five paragraphs mayoptionally have a U-value of no greater than 0.253, even more preferablyno greater than 0.249, with an example range from 0.244 to 0.253BTU/hr-ft²-° F.

The IG window unit of any of the preceding six paragraphs may optionallyhave a ratio calculated as SHGC/U-Value of at least 2.10, morepreferably of at least 2.20, and most preferably of at least 2.24.

In the IG window unit of any of the preceding seven paragraphs, one orboth of the first and second upper contact layers may comprise an oxideof Ni and/or Cr (e.g., NiCrOx).

The IG window unit of any of the preceding eight paragraphs mayoptionally further comprise: (a) a layer comprising tin oxide locatedbetween and directly contacting the layer comprising zinc stannate andthe second lower contact layer comprising zinc oxide, or (b) a layercomprising niobium oxide located between and directly contacting thelayer comprising zinc stannate and the second lower contact layercomprising zinc oxide. Regarding (a) for example, the layer comprisingtin oxide may be doped with other material such as Al, Bi or the like.

In the IG window unit of any of the preceding nine paragraphs thedielectric layer comprising titanium oxide may be located under anddirectly contacting the first lower contact layer comprising zinc oxide.

The IG window unit of any of the preceding ten paragraphs the dielectriclayer located over the second upper contact layer may comprise tin oxideand/or silicon nitride.

In certain example embodiments of this invention, there is provided aninsulating glass (IG) window unit comprising: first and second glasssubstrates that are spaced apart from each other with a gap therebetweenand substantially parallel to each other, wherein the first glasssubstrate is adapted to be at a building exterior and the second glasssubstrate is adapted to be closer to a building interior than is thefirst glass substrate; a low-E coating on a major surface of the secondglass substrate facing said gap; the low-E coating comprising, movingaway from the second glass substrate: (a) a dielectric layer; (b) afirst lower contact layer comprising zinc oxide; (c) a first IRreflecting layer comprising silver located over and directly contactingthe first lower contact layer; (d) a first upper contact layer locatedover and directly contacting the first IR reflecting layer comprisingsilver; (e) a layer comprising tin oxide and/or zinc stannate; (f) asecond lower contact layer comprising zinc oxide; (g) a second IRreflecting layer comprising silver located over and directly contactingthe second lower contact layer; (h) a second upper contact layer locatedover and directly contacting the second IR reflecting layer comprisingsilver; and (i) another dielectric layer; wherein the low-E coating hasa normal emissivity of no greater than 0.04; wherein a ratio of athickness of the first IR reflecting layer comprising silver to athickness of the second IR reflecting layer comprising silver,calculated as the thickness of the first IR reflecting layer comprisingsilver divided by the thickness of the second IR reflecting layercomprising silver, is from 0.30 to 0.50; and wherein the IG window unithas each of: (i) a visible transmission of at least about 69.5%, (ii) anSHGC value of at least 0.50, (iii) an outside visible reflectance of nogreater than 15%, and (iv) a U-value of no greater than 0.253BTU/hr-ft²-° F.

The IG window unit of the immediately preceding paragraph may optionallyhave a ratio calculated as SHGC/U-Value of at least 2.0.

The IG window unit of any of the preceding two paragraphs may optionallyhave an SHGC value of at least 0.52, more preferably of at least 0.54,and most preferably of at least 0.56.

The IG window unit of any of the preceding three paragraphs mayoptionally have only one low-E coating.

The IG window unit of any of the preceding four paragraphs mayoptionally have a U-value of no greater than 0.251 BTU/hr-ft²-° F.

The IG window unit of any of the preceding five paragraphs mayoptionally have a ratio calculated as SHGC/U-Value of at least 2.10,more preferably of at least 2.20, and still more preferably of at least2.24. For example, an example of this invention has a U-value of 0.251and an SHGC of 0.57, which results in a ratio SHGC/U-Value of 2.27.

In the IG window unit of any of the preceding six paragraphs, both ofthe first and second upper contact layers may comprise an oxide of Niand/or Cr.

In the IG window unit of any of the preceding seven paragraphs the layercomprising tin oxide and/or zinc stannate may comprise or consistessentially of zinc stannate and may be located between and contactingthe first upper contact layer and a layer comprising tin oxide.

In the IG window unit of any of the preceding eight paragraphs the low-Ecoating may further comprise a layer comprising titanium oxide locatedbetween the first IR reflecting layer and the second glass substrate.

In the IG window unit of any of the preceding nine paragraphs the ratioof the thickness of the first IR reflecting layer comprising silver tothe thickness of the second IR reflecting layer comprising silver,calculated as the thickness of the first IR reflecting layer comprisingsilver divided by the thickness of the second IR reflecting layercomprising silver, may be from 0.38 to 0.47.

While the invention has been described in connection with what ispresently considered to be the most practical and preferred embodiment,it is to be understood that the invention is not to be limited to thedisclosed embodiment, but on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

The invention claimed is:
 1. A coated article including a low-emissivity(low-E) coating on a substrate, the low-E coating comprising, movingaway from the substrate: a dielectric layer; a dielectric layercomprising metal oxide; a first lower contact layer; a first IRreflecting layer comprising silver located over and directly contactingthe first lower contact layer; a first upper contact layer comprisingmetal oxide located over and directly contacting the first IR reflectinglayer comprising silver; a layer comprising zinc stannate located overand directly contacting the first upper contact layer comprising metaloxide; a layer consisting essentially of tin oxide located over anddirectly contacting the layer comprising zinc stannate; a second lowercontact layer consisting essentially of zinc oxide, which may optionallybe doped with aluminum, located over and directly contacting the layerconsisting essentially of tin oxide; wherein a total thickness of thelayer comprising zinc stannate and the layer consisting essentially oftin oxide is from 600-900 Å; a second IR reflecting layer comprisingsilver located over and directly contacting the second lower contactlayer; a second upper contact layer located over and directly contactingthe second IR reflecting layer comprising silver; and a dielectriclayer; wherein the low-E coating has only two IR reflecting layerscomprising silver, and wherein the low-E coating has a normal emissivityof no greater than 0.04; wherein a ratio of a thickness of the first IRreflecting layer comprising silver to a thickness of the second IRreflecting layer comprising silver, calculated as the thickness of thefirst IR reflecting layer comprising silver divided by the thickness ofthe second IR reflecting layer comprising silver, is from 0.30 to 0.50;and wherein the coated article, measured monolithically, has a visibletransmission of at least about 70% and/or a film side visiblereflectance of no greater than 6.5%.
 2. An IG window unit comprising thecoated article of claim
 1. 3. A coated article including alow-emissivity (low-E) coating on a substrate, the low-E coatingcomprising, moving away from the substrate: a dielectric layer; adielectric layer comprising metal oxide; a first lower contact layer; afirst IR reflecting layer comprising silver located over and directlycontacting the first lower contact layer; a first upper contact layercomprising metal oxide located over and directly contacting the first IRreflecting layer comprising silver; a layer comprising zinc stannatelocated over and directly contacting the first upper contact layercomprising metal oxide; a layer consisting essentially of tin oxidelocated over and directly contacting the layer comprising zinc stannate;a second lower contact layer consisting essentially of zinc oxide, whichmay optionally be doped with aluminum, located over and directlycontacting the layer consisting essentially of tin oxide; wherein atotal thickness of the layer comprising zinc stannate and the layerconsisting essentially of tin oxide is from 600-900 Å; a second IRreflecting layer comprising silver located over and directly contactingthe second lower contact layer; a second upper contact layer locatedover and directly contacting the second IR reflecting layer comprisingsilver; and a dielectric layer; wherein the low-E coating has only twoIR reflecting layers comprising silver; wherein a ratio of a thicknessof the first IR reflecting layer comprising silver to a thickness of thesecond IR reflecting layer comprising silver, calculated as thethickness of the first IR reflecting layer comprising silver divided bythe thickness of the second IR reflecting layer comprising silver, isfrom 0.30 to 0.50; and wherein the coated article, measuredmonolithically, has a visible transmission of at least about 70% and/ora film side visible reflectance of no greater than 6.5%.
 4. The coatedarticle of claim 3, wherein the coated article, measured monolithically,has both a visible transmission of at least about 70% and a film sidevisible reflectance of no greater than 6.5%.
 5. An IG window unitcomprising the coated article of claim
 4. 6. The coated article of claim3, wherein the first lower contact layer comprises zinc oxide.
 7. Thecoated article of claim 3, wherein the first upper contact layercomprises oxide of Ni and Cr.
 8. The coated article of claim 3, whereinthe second upper contact layer comprises oxide of Ni and Cr.
 9. Thecoated article of claim 8, wherein the first upper contact layercomprises oxide of Ni and Cr.